Ante-Nicene Fathers, Vol III:
Tertullian: Part II: The Mystery of the Assumption of Our Perfect Human Nature by the Second Person of the Blessed Trinity. He is Here Called, as Often Elsewhere, the Spirit.

p. 537Chapter XVIII.—The Mystery of the Assumption of Our Perfect Human Nature by the Second Person of the Blessed Trinity. He is Here Called, as Often Elsewhere, the Spirit.

Now, that we may give a simpler answer, it was not fit that the Son of God should be born of a human fathers seed, lest, if He were wholly the Son of a man, He should fail to be also the Son of God, and have nothing more than “a Solomon” or “a Jonas,” 7186
—as Ebion 7187
thought we ought to believe concerning Him. In order, therefore, that He who was already the Son of God—of God the Fathers seed, that is to say, the Spirit—might also be the Son of man, He only wanted to assume flesh, of the flesh of man 7188
without the seed of a man; 7189
for the seed of a man was unnecessary 7190
for One who had the seed of God. As, then, before His birth of the virgin, He was able to have God for His Father without a human mother, so likewise, after He was born of the virgin, He was able to have a woman for His mother without a human father. He is thus man with God, in short, since He is mans flesh with Gods Spirit 7191
—flesh (I say) without seed from man, Spirit with seed from God. For as much, then, as the dispensation of Gods purpose 7192
concerning His Son required that He should be born 7193
of a virgin, why should He not have received of the virgin the body which He bore from the virgin? Because, (forsooth) it is something else which He took from God, for “the Word” say they, “was made flesh.” 7194
Now this very statement plainly shows what it was that was made flesh; nor can it possibly be that 7195
anything else than the Word was made flesh. Now, whether it was of the flesh that the Word was made flesh, or whether it was so made of the (divine) seed itself, the Scripture must tell us. As, however, the Scripture is silent about everything except what it was that was made (flesh), and says nothing of that from which it was so made, it must be held to suggest that from something else, and not from itself, was the Word made flesh. And if not from itself, but from something else, from what can we more suitably suppose that the Word became flesh than from that flesh in which it submitted to the dispensation? 7196
And (we have a proof of the same conclusion in the fact) that the Lord Himself sententiously and distinctly pronounced, “that which is born of the flesh is flesh,” 7197
even because it is born of the flesh. But if He here spoke of a human being simply, and not of Himself, (as you maintain) then you must deny absolutely that Christ is man, and must maintain that human nature was not suitable to Him. And then He adds, “That which is born of the Spirit is spirit,” 7198
because God is a Spirit, and He was born of God. Now this description is certainly even more applicable to Him than it is to those who believe in Him. But if this passage indeed apply to Him, then why does not the preceding one also? For you cannot divide their relation, and adapt this to Him, and the previous clause to all other men, especially as you do not deny that Christ possesses the two substances, both of the flesh and of the Spirit. Besides, as He was in possession both of flesh and of Spirit, He cannot possibly, when speaking of the condition of the two substances which He Himself bears, be supposed to have determined that the Spirit indeed was His own, but that the flesh was not His own. Forasmuch, therefore, as He is of the Spirit He is God the Spirit, and is born of God; just as He is also born of the flesh of man, being generated in the flesh as man. 7199